1. Field of the Invention
The present invention relates to a semiconductor device, more particularly to a protection element to protect an internal circuit of a semiconductor device.
2. Description of the Related Art
In recent years, in order to protect the internal circuit of an IC from current of electrostatic surge, a protection element is provided for the input terminal. As this protection element, a diode with a high breakdown voltage is generally used. FIGS. 1A and 1B show such a conventional high breakdown voltage diode. Referring to FIGS. 1A and 1B, in the conventional diode, a P-type well 801 is formed in a P-type semiconductor substrate 800, and a P+-type diffusion layer 803 is formed in a ring along an outer circumference of the P-type well 801 to have a higher impurity concentration than the P-type well 801. An N+-type diffusion layer 804 is formed in a region of the P-type well 801 surrounded by the P+-type diffusion layer 803. It should be noted that the P+-type diffusion layer 803 and the N+-type diffusion layer 804 separated by an element separation region (insulation region) 802, and contacts 805 are formed on the respective diffusion layers to form an anode and a cathode. In this way, in the conventional high breakdown voltage diode, the breakdown voltage is improved by forming the large N+-type diffusion layer 804. For example, such a conventional example is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 1-214055)
However, in the structure of the above-mentioned conventional high breakdown voltage diode, in order to need a large region for improvement of the breakdown voltage, the high integration becomes difficult.